An immobilizer is well-known as technology for preventing the theft of vehicles and the like. This technology only permits the engine of a vehicle to be started when an ID code transmitted by an IC chip inside the vehicle key matches an ID code of an engine control device inside the vehicle, and disallows operation of the engine using copied keys or any key that is not the authorized key containing the ID code, thereby preventing theft.    Patent Document 1: Japanese Patent No. 3204006